There were only a small number of games that supported any of the Apple II sound cards such as the Mockingboard.

From those games that used the Mockingboard, did any of them utilize the on-board VIA's timers or interrupts for anything?

Or, were all of the games straight PORT A/B access from the CPU?

From the schematics I've seen, the IRQ line is attached to one VIA and the NMI is attached to the other VIA. But I have no idea if any games utilized them.


1 Answer 1


Yes, games like Rescue Raiders and Silent Service used interrupts to queue music and sound effects while other things were happening on the screen. Perhaps the best example of the technique is Skyfox, which had music playing during the frenetic dogfight action.

The option to have simultaneous graphics and great sound without cycle-counting was one of the biggest gains that the Mockingboard offered, apart from the sound options themselves.

In contrast, the game Microwave interleaved the animation and sound effects by careful cycle-counting. The game Nemesis interleaved user-interaction with the music in the same way. This programming model limited the features that could be included because of the challenge to maintain all code-paths that toggled the speaker at the right time.

  • 1
    Thanks for the great answer! I have accepted this as the answer. I was, however, wondering if you had any references to these? I'd like to study the code more if I could. Thanks!
    – cbmeeks
    Feb 13, 2017 at 12:12
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    all four games are freely (as opposed to free - they are still copyrighted material) available from the same site. Feb 14, 2017 at 22:36

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